Cable television networks such as those provided by Comcast Cable Communications, Inc., of Philadelphia, Pa., Cox Communications of Atlanta Ga., Time-Warner Cable, of Marietta Ga., Continental Cablevision, Inc., of Boston Mass., and others, provide cable television services to a large number of subscribers over a large geographical area. The cable television networks typically are interconnected by cables such as coaxial cables or a Hybrid Fiber/Coaxial (“HFC”) cable system which have data rates of about 10 Mega-bits-per-second (“Mbps”) to 30+ Mbps.
The Internet, a world-wide-network of interconnected computers, provides multi-media content including audio, video, graphics and text that requires a large bandwidth for downloading and viewing. Most Internet Service Providers (“ISPs”) allow customers to connect to the Internet via a serial telephone line from a Public Switched Telephone Network (“PSTN”) at data rates including 14,400 bps, 28,800 bps, 33,600 bps, 56,000 bps and others that are much slower than the about 10 Mbps, to 30+ Mbps available on a coaxial cable or HFC cable system on a cable television network. Further, the ISPs allow customers to connect to the Internet via other types of connections, such as a Digital Subscriber Line (“DSL”) connection providing data transmission rates from 512 kbps to 1.544 Mbps downstream and about 128 kbps upstream, or an Asymmetric Digital Subscriber Line (“ADSL”) connection providing data transmission rates up to 6.1 Mbps downstream and 640 kbps upstream.
With the explosive growth of the Internet, many customers have desired to use the larger bandwidth of a cable television network to connect to the Internet and other computer networks. Cable modems, such as those provided by 3Com Corporation of Santa Clara, Calif., Motorola Corporation of Arlington Heights, Ill., Cisco Corporation of San Jose, Calif., Scientific-Atlanta, of Norcross, Ga., and others, offer customers higher-speed connectivity to the Internet, an intranet, Local Area Networks (“LANs”) and other computer networks via cable television networks. These cable modems currently support a data connection to the Internet and other computer networks via a cable television network with a data rate of up to 30+ Mbps, which is a much larger data rate than can be supported by a modem used over a serial telephone line.
Many cable television networks provide bi-directional cable systems, in which data is sent “downstream”, from a “headend” to a customer, as well as “upstream”, from the customer back to the headend. The cable system headend is a central location in the cable television network and, further, is responsible for sending cable signals in the downstream direction and receiving cable signals in the upstream direction. An exemplary data-over-cable system with RF return typically includes customer premises equipment entities such as a customer computer, a cable modem, a cable modem termination system, a cable television network, and a data network such as the Internet.
Some cable television networks provide only uni-directional cable systems, supporting only a “downstream” data path, which provides a path for flow of data from a cable system headend to a customer. A return data path via a telephone network, such as a public switched telephone network provided by AT&T and others, (i.e., a “telephone return”) may be used for an “upstream” data path, which provides a path for flow of data from the customer back to the cable system headend. A cable television system with an upstream connection to a telephone network is typically called a “data-over-cable system with telephony return.”
An exemplary data-over-cable system with a telephony return typically includes customer premises equipment (“CPE”) entities (such as a customer computer or a Voice over Internet Protocol (“VoIP”) device), a cable modem, a cable modem termination system, a cable television network, a public switched telephone network, a telephone remote access concentrator, and a data network (e.g., the Internet). The cable modem termination system and the telephone remote access concentrator combined are called a telephone return termination system.
In a bi-directional cable system, when the cable modem termination system receives data packets from the data network, the cable modem termination system transmits received data packets downstream via the cable television network to a cable modem attached to a customer premises equipment entity. The customer premises equipment entity sends response data packets to the cable modem, which sends the response data packets upstream via the cable network. The cable modem termination system sends the response data packets back to the appropriate host on the data network.
In the case of a telephony return system, when a cable modem termination system receives data packets from a data network, the cable modem termination system transmits the received data packets downstream via a cable television network to a cable modem attached to a customer premises equipment entity. The customer premises equipment entity sends response data packets to the cable modem, which sends response data packets upstream via a public switched telephone network to a telephone remote access concentrator. Next, the telephone remote access concentrator sends the response data packets back to the appropriate host on the data network.
When a cable modem used in a cable system is initialized, the cable modem establishes a communication link to a cable modem termination system via a cable network and, in telephony return data-over-cable systems to a telephone return termination system via a public switched telephone network. As the cable modem is initialized, the cable modem initializes one or more downstream channels via the cable network. Also upon initialization, the cable modem receives a configuration file (a boot file) from a configuration server via a trivial file-transfer protocol (“TFTP”) exchange process.
As the theft of service is becoming a vital concern for cable network operators, a few standards have been developed to provide cable operators with basic protection from the theft of service. These standards, among others, include a Data-Over-Cable-Service-Interface-Specification (“DOCSIS”) Baseline Privacy Interface (“BPI”) Specification and a Data-Over-Cable-Service-Interface-Specification (“DOCSIS”) Baseline Privacy Plus Interface (“BPI+”) Specification. The Baseline Privacy Interface Specification is currently utilized in data-over-cable networks, while the Baseline Privacy Plus Interface Specification products are currently being developed and tested.
The Baseline Privacy Interface Specification provides cable modem users with data privacy across a network by encrypting data flow between cable modems and headend entities such as a cable modem termination system. The secondary goal of the Baseline Privacy is to provide cable operators with a basic protection from the theft of service. Since the data privacy is the primary service goal of that specification, and given that neither a cable modem nor a cable modem termination system authentication is a prerequisite for providing the data privacy, the Baseline Privacy's key distribution protocol does not authenticate cable modems and cable modem termination systems, i.e., it does not employ authentication mechanisms such as passwords or digital signatures. In the absence of authentication, the Baseline Privacy provides a basic service protection by ensuring that a cable modem, uniquely identified by its 48-bit physical (Medium Access Control “MAC”) address, can only obtain keying material for services it is authorized to use.
The Baseline Privacy Plus Interface (“BPI+”) specification describes Medium Access Control layer security services for cable modems and cable modem termination systems that interact based on standards proposed by the Data-Over-Cable-Service-Interface Specification (“DOCSIS”). Specifically, the Baseline Privacy Plus provides cable modem users with the data privacy across the cable networks and prevents unauthorized users from gaining access to the network services. The Baseline Privacy Plus specification proposes a key management protocol providing a service protection by adding a digital-certificate-based cable modem authentication.
According to the basic operation of the Baseline Privacy Plus, a cable modem has an internally installed digital certificate issued by a cable modem manufacturer. A digital certificate is an electronic version of an identification card that establishes credentials and authenticates communication between two network entities. One of the widely used standards for defining digital certificates includes a X.509 digital certificate standard. For more information on the X.509 security certificates, see the Request For Comments (“RFC”) 2459, “Internet X.509 Public Key Infrastructure Certificate and CRL Profile,” by R. Housley, W. Ford, W. Polk, and D. Solo, incorporated herein by reference. The digital certificate issued by the manufacturer includes a cable modem's public key and a physical (MAC) address. The digital certificate may further include a manufacturer's signature that binds the MAC address of the cable modem with its keying data such as its public key. When the cable modem receives the digital certificate, the cable modem may use the signature specified in the certificate to authenticate the received digital certificate. Certificates received on cable modems may also include different identifying information such as a manufacturer's identifier. When a cable modem requests authorization from a cable modem termination system, the cable modem presents its digital certificate that is then verified on the cable modem termination system. Upon a successful verification of the digital certificate, the cable modem termination system typically uses the public key specified in the certificate to encrypt an authorization key, which is then sent to the cable modem requesting authorization.
According to the Baseline Privacy Plus specification, a cable modem termination system associates a cable modem's authenticated identity to a paying subscriber and to data services that the subscriber is authorized to access. Therefore, with the authorization key exchange, the cable modem termination system establishes an authenticated identity of a client cable modem and network services that the cable modem is authorized to access. Further, since the cable modem termination system authorizes cable modems, system resources are protected from attacks of hacker cable modems masquerading the identity of legitimate cable modems. Further, the use of digital certificates prevents unauthorized cable modems from passing fake credentials to the cable modem termination system.
The assumption of the Baseline Privacy Plus specification is that cable modems would be manufactured with installed digital certificates. However, such an assumption creates a problem for cable modems already deployed in data-over-cable systems, as for those cable modems to run in the Baseline Privacy Plus mode, they need to obtain digital certificates. A number of methods for providing digital certificates to cable modems are described in the existing Data-Over-Cable-Service-Interface-Specification standards. One of such methods employs management protocols to download a digital certificate to a cable modem. Using the proposed methods, a cable operator may use one of the existing network management protocols to retrieve a physical (MAC) address and a public key from a cable modem, and, subsequently, send the retrieved data to a cable modem's manufacturer. Upon a receipt of the cable modem's data, the manufacturer may create a digital certificate for the cable modem and send it to the cable modem operator. Then, the cable modem operator may employ the network management protocols to load the certificate on the cable modem.
The existing method for providing digital certificates has several drawbacks. First, it requires a cable operator to retrieve authentication and configuration information from cable modems and then format the retrieved data according to the manufacturers' standards. Further, it requires a lot of coordination between cable operators and manufacturers, and, lastly, it does not guarantee that all of cable modems intended for an upgrade will actually get upgraded since some of the cable modems may be offline or in the inventory when the process is run by a cable operator.
Therefore, it is still desirable to develop a system and method for providing digital certificates to network entities such as cable modems in a data-over-cable system.